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Abstract

This study investigated the location, habitat preferences, and diel movements of burbot (lota lota) and salmonids in a small tributary stream in late spring, early summer. The research provides base-line information on fish distribution prior to the replacement of a culvert and reconnection of upstream reaches. The tributary was divided into six 100-meter reaches using blocker nets and data was collected using mark-recapture and electrofishing techniques. The community was dominated by coho (Oncorhynchus kisutch) and chinook salmon (Oncorhynchus tshawytscha), rainbow trout (Salmo gairdneri), northern mottled sculpin (Cottus bairdii bairdii), brook lamprey (Ichthyomyzon fosser), and the burbot. Salmonids favored undercut banks during the day (p=0.014) and woody debris at night (p=0.017, ANOVA). Substrate was dominated by sand thus the bulk of aquatic macroinvertebrate production was likely occurring on large woody debris—the area preferred by the fish at dusk and at night. In addition, water depth was positively correlated to fish density (R2 = 0.73; p=0.031, step-wise MLR). Like the salmonids, burbot preferred undercut banks and abundance appeared to increase at night—a pattern observed in all major fish species with the exception of the chinook salmon, although trends were not significant for any species. The majority of captured fish were juvenile, and we hypothesize that at these early life-history stages, the fish are moving into the tributary system at dusk to avoid predation pressure in the main channel. The coho population decreased through time (p=0.034) while rainbow trout YOY increased (p=0.039). There was no recapture of fin-clipped rainbow trout (year one plus) indicating a high degree of turnover with the main channel, likely as a result of the culvert.